Alarms can be used in a wide variety of applications including where it is important to be able to pinpoint the location of the alarm, such as, in reversing vehicles, medical emergencies, and in hardware devices that use Bluetooth or other wireless communications protocols in combination with mobile software applications to locate lost items.
Sound localization is the listener's ability to locate a sound's origin in terms of direction and distance via auditory signals alone. The human auditory system uses several cues obtained from the sounding source to establish sound localization. The cues and theories leveraged to establish localization include but are not limited to Interaural Time differences (ITD), Interaural Intensity differences (IIDs), Head Related Transfer Function (HRTF), Correlation Theory, Pinna Filtering, the Franssen Effect and the Precedence Effect. The more cues that a sound source accurately establishes to a listener, the greater the confidence level that a sounding source establishes sound localization to the listener. All acoustic waveforms achieve some level of localization but maximizing the confidence levels of each cue establishes a much greater degree of certainty within the listener.
The Precedence Effect or Law of the First-Arriving Wavefront is a binaural psychoacoustic effect. When a sound is followed by another relatively similar sound separated by a sufficiently short time delay below the listener's echo threshold, listeners perceive a single auditory event; the event's perceived spatial location is dominated by the location of the first-arriving acoustic waveform generated by the sounding device. Often, this law applies to waveforms generated by reverberation off of physical medium. The lagging sound also affects the perceived location but is suppressed by the first-arriving sound.
Acoustic reverberation off walls and physical mediums greatly affects a listener's ability to accurately determine localization cues. When an output frequency does not complete the full propagation wavelength against a physical medium, the medium does not absorb most of the acoustic waveform but instead reflects the waveform to enable the waveform to complete. The waveform continues to be present in the acoustic environment consequently as the waveform will continue to vibrate through the sounding medium, typically air, posing an issue to localization as the new source for this reverberated waveform is off a physical medium instead of the sound originator.
The Precedence Effect in theory should dictate how the reverberation should be ignored by the listeners acoustic localization system but further experimentation after the establishment of the Precedence Effect has shown that the greater the presence of reverberation, the lesser the level of certainty for an alarm to be localized. Although the Precedence Effect is a well-known phenomenon, minimizing the necessity of the Precedence Effect enhances localization.
Interaural Time Differences, or ITDs, are established by the different arrival time sound takes to reach each ear. For a sounding source to achieve an optimal ITDs cue, low frequency waveforms typically below 1500 Hz with long wavelengths should be present, as a longer wavelength takes a sufficiently long amount of time to complete the distance between each ear, translating to a greater phase shift of the original waveform at the complementary ear.
Interaural Intensity Differences, or IIDs, are established by the different loudness levels of the sound as it reaches each ear. For a sounding source to achieve an optimal IID cue, high frequency waveforms with short wavelengths typically above 5500 Hz should be present as short wavelengths are greatly attenuated by physical impediments, which in this situation, is the listeners head.
The Head Related Transfer Function, or HRTF, is the transfer function relating how the head manipulates the input waveform as the sound passes through the head and ear pinna or Pinna Filtering. For a sounding source to achieve an optimal HRTF cue, the transfer function must establish as varied of a response as possible between the originating waveform and the perceived waveform.
A tone's fast attack onset relates to the efficacy of the Franssen Effect as a localization illusion masking a sound's origination. The Franssen Effect dictates the timing interval from a tone's original generation to a tone's full waveform reproduction, known as attack onset. Attack onset has been shown in studies to affect the human ability to establish acoustic cues. A slower attack onset enables a greater level of certainty to be established and minimizes the Franssen Effect. The theory why a slower attack onset enables greater certainty and minimizes the Franssen Effect is that the reverberant field of the room or space in which the sound is being heard has yet to be fully realized relative to the direct sound source.
There have been prior art solutions for developing pinpoint alarms that include RE 44,912, which describes an alarm is implemented with a simple electronic circuit that uses a zener diode as a signal generator, and emits pulses of broadband sound, which permit the human brain to better pinpoint the location of the sound source than is possible with single tone.
U.S. Pat. No. 9,445,171 describes another prior art pinpoint alarm solution in which a sounder for use in a mobile apparatus that comprises an electrostatic generator and an electrostatic transducer generates an audible sound comprising continuous repetitions of a pre-determined section of substantially broadband sound ranging within the full auditory spectrum and may be considered broadband as well.
Broadband acoustic sound is produced from a wide spread of frequencies within the range of audible frequencies. By contrast, narrow band sound is produced from a smaller range of frequencies defined within a specific interval.
U.S. Pat. No. 9,445,171 states that its methods may be applied to any type of sound: broadband, narrow band or another type. However, in considering the clues and theories leveraged to establish localization, the inventor has determined that alarms structured differently than the prior art pinpoint alarm solutions, such as U.S. Pat. No. 9,445,171 and RE 44,912 that rely upon continuous repetitions of broadband sound have advantages.
As described in greater detail herein below, the inventor has determined that alarms structured with a piezoelectric plate and Helmholtz resonator cavity that generate narrow band peaks based off a predetermined frequency interval can provide an increased localization certainty and be reproduced with acoustic transducer elements which have response curves capable of reproducing sound at a valuable loudness level within the above defined frequency interval.